1) Field of the Invention
The present invention relates to a liquid crystal display unit that functions as both a reflective type liquid crystal display unit and a transmissive type liquid crystal display unit.
2) Description of the Related Art
Generally, a portable information device includes a transmissive type liquid crystal display unit that has no light emitting function, and performs a display using light from a light source incorporated in the device. The device can include, other than the transmissive type liquid crystal display unit, a reflective type liquid crystal display unit that performs a display using light from the outside, or a transflective type liquid crystal display unit that has both functions of the transmission and the reflective types, and the like.
In the transflective type liquid crystal display unit, a reflection film that has a plurality of reflectors having a small transmission factor and a plurality of apertures having a large transmission factor is formed on one of a pair of substrates that sandwich a liquid crystal layer, on the surface of the substrate facing the liquid crystal layer. The display unit functions as a reflective type display unit by using light that is incident from the outside to a liquid crystal display element and reflected by the reflection film with a reflection characteristic. The display unit also functions as a transmissive type display unit by using light that is emitted from the light source within the device and that passes through the aperture of the reflection film. FIG. 22 is a cross-section of a conventional transflective type liquid crystal display unit.
A liquid crystal layer 18 is filled in a space between a first substrate 1 and a second substrate 5, and the space is sealed. A first electrode 2 and an orientation film 27 made of a transparent electric conductive film are provided on the surface of the first substrate 1 facing the liquid crystal layer 18. A reflection film 21 having a reflector made of an aluminum film is provided on the surface of the second substrate 5 facing the liquid crystal layer 18. An aperture 22 is provided on the reflection film 21. A light transmission factor of the aperture 22 is larger than that of the reflector (that is, the aluminum film part) of the reflection film 21. The reflection film 21 is covered with an insulation film 23 made of acrylic resin. A second electrode 6 and an orientation film 28 made of a transparent electric conductive film are provided on the surface of the insulation film 23. Each area in which the first electrode 2 and the second electrode 6 overlap each other corresponds to a pixel. Each pixel is provided with the reflector and the aperture of the reflection film.
The first substrate 1 and the second substrate 5 are adhered to each other using a sealing member 16, with a predetermined gap therebetween. A space surrounded by the first substrate 1, the second substrate 5, and the sealing member 16, is sealed with a sealer (not shown), including the liquid crystal layer 18 therein. An upper polarizing film 31 is provided on the surface of the first substrate 1 at an observer side, that is, on the surface opposite to the liquid crystal layer 18. A retardation film 34 is provided on the surface of the second substrate 5 opposite to the liquid crystal layer 18. A lower polarizing film 45 is provided on the surface of the retardation film 34. The retardation film 34 and the lower polarizing film 45 are adhered to each other with a transparent adhesive material (not shown).
A backlight 41 having a backlight reflection film 42 is provided as an auxiliary light source at a lower side of the lower polarizing film 45. Light emitted from the backlight 41 is directly incident to the aperture 22 of the reflection film 21 and passes through the liquid crystal layer 18, to become a first transmission light-flux 55 that is output to the observer side. The light from the backlight 41 also repeats reflection from the reflector of the reflection film 21, and a reflection from the backlight 41 or the backlight reflection film 42, reaches the aperture 22, then passes through the aperture 22 and the liquid crystal layer 18, to become a second transmission light-flux 56 that is output to the observer side.
Each time when the light that becomes the second transmission light-flux 56 repeats a reflection between the reflector of the reflection film 21 and the backlight reflection film 42, the light passes through the lower polarizing film 45, and is slightly absorbed by the lower polarizing film 45. Therefore, the light that becomes the second transmission light-flux 56 gradually loses intensity while being reflected between the reflector of the reflection film 21 and the backlight reflection film 42. As a result, the light becomes weak when the light is output to the observer side as the second transmission light-flux 56. On the other hand, an incident light 51 from the outside passes through the liquid crystal layer 18, is reflected from the reflector of the reflection film 21, passes through the liquid crystal layer 18 again, and is output to the observer side as a reflection light 52.
In the transflective type liquid crystal display unit, light utilization efficiency, and thereby efficiency of outputting the light emitted from the backlight to the observer side, has been improved by providing a reflection polarizing film between the lower polarizing film and the backlight, and by disposing the transmission polarization axis of the reflection polarizing film and the transmission polarization axis of the lower polarizing film in parallel (for example, see Japanese Patent Application National Publication No. H09-506984). Of the light that is emitted from the backlight, the light that is incident to the reflection polarization axis of the reflection polarizing film is reflected from the reflection polarizing film and returns to the backlight. Subsequently, a polarization cancellation and a reflection occur on the backlight, and the backlight emits light again to the reflection polarizing film.
A part of the light parallel with the transmission polarization axis of the reflection polarizing film is directly output from the aperture of the reflection film. The light that is incident to the reflector of the reflection film is reflected from the reflector of the reflection film to the reflection polarizing film side, and is then reflected by the reflection polarizing film. As explained above, the light reflected by the reflection polarizing film and the light reflected by the backlight are mixed, and the mixed light is output to the observer side, thereby increasing the amount of the light output to the observer side, and realizing bright display.
Furthermore, a transmissive type liquid crystal display unit has been suggested to improve brightness of the reflection light and the transmission light-flux from the transflective type liquid crystal display unit. The transmissive type liquid crystal display unit has a polarizing film (that is, an embedded polarizing film) on the surface of the second substrate facing the liquid crystal layer (for example, see Page 3 and FIG. 7 of Japanese Patent Application Laid-Open No. 2003-302628). Another liquid crystal display unit having a reflection polarization layer that has plural fine slit apertures provided on a metal reflection film, is also proposed (for example, see Pages 2 and 3 of Japanese Patent Application Laid-Open No. 2003-228059).
However, the configuration disclosed in the Japanese Patent Application National Publication No. H09-506984 is not preferable for thinning and weight saving, which are important for compact portable devices, and thereby increasing cost. Besides, since the reflection polarizing film and the transmission polarization axis of an absorption polarization axis need to be laminated in alignment, a yield ratio can be reduced due to dusts and foreign matter between both polarizing films. Further, colors can change due to an in-plane variance of polarization degrees of the reflection polarizing film, particularly due to a variance of polarization degrees in a visible light area, which can lead to a change in display colors.
An absorption polarizing film and a reflection polarizing film are laminated in this order, even if a reflection film having an aperture is used, on the second substrate that is provided at the backlight side, which increases cost. There are also problems of a generation of dusts at the lamination time, and a generation of loss due to light absorption by the absorption polarizing film. Further, since the backlight needs to have the polarization cancellation function and the reflection function, the backlight configuration has no degree of freedom, and cost increase and performance reduction occur due to the addition of functions. On the other hand, the configuration disclosed in the Japanese Patent Application Laid-Open No. 2003-302628 has many problems yet to be solved regarding a setting position of the embedded polarizing film and a combination with other components.